1. Field of the Invention
This invention relates to vortex structure suppression and related noise reduction due to vortices generated by eductors particularly as applied to aircraft gas turbine engine sensor scoops and mounts.
2. Description of Related Art
The present invention relates to eductors in the form of scoops surrounding sensor assemblies used for sampling a flowstream and particularly an airstream flowing adjacent to a boundary layer in an aircraft in order to measure airstream characteristics such as temperature and pressure. Although the invention was designed for use in nacelle inlets of gas turbine engines it is not limited in scope to such applications as will be seen further herein.
Typically in the past, measurement of the airstream's characteristics, such as temperature, pressure, and velocity, was provided by the use of various types of probes. Such probes are typically mounted within a mast that extended from the inner surface of an aircraft gas turbine engine nacelle into the airstream in order to position the sensing element of the probe outside the airstream's boundary layer. Boundary layers have vastly different characteristics than incoming airstreams (often referred to as freestream air) and so one must carefully try to avoid measuring boundary layer characteristics instead of freestream air characteristics.
Foreign object damage (often referred to as FOD) was another problem encountered by these type of sensors. Sensors and the probes are particularly susceptible to damage caused by being struck by incoming objects such as birds, insects, ice particles, and miscellaneous types of debris. Rain water also poses a problem because, though it may not causes physical damage to the probe, rain does tend to alter measurements taken by temperature probes.
For these reasons an airstream eductor for use as a sensor scoop was developed as described in U.S. Pat. No 4,644,806, entitled "Airstream Eductor" by Elgin E. Flagg and Melvin Bobo, which issued Feb. 24, 1987 and assigned to General Electric, the same assignee as in the present invention, and incorporated herein by reference. The Flagg invention provides a diffusing channel recessed into the inner surface of the nacelle for diverting boundary layer air from a probe and inducing freestream air to impinge upon the probe.
However, vortices are generated that coalesce into vortex filaments that, besides enhancing the eductors operation, travel downstream into the gas turbine engine's fan causing loud and undesirable noise to be generated. The present invention is directed at reducing fan velocity distortion and this noise.